rtw88: 8821c: add power tracking

The TX power requires to be adjusted based on the thermal value.
The actual power will decrease if the thermal value raised, and
will increase if the thermal value lowered. Driver comapres the
thermal value, as moving averages. If it changes over a limit,
driver will modify the TX power index to compensate.

Implement rtw_chip_ops::pwr_track() for 8821c.

Signed-off-by: Tzu-En Huang <tehuang@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200603094218.19942-3-yhchuang@realtek.com